The system in accordance with the present invention is operated preferably in the brake-by-wire operating mode and can be operated in at least one fall-back operating mode in which only operation by the vehicle driver is possible, having:
a) a brake pedal for actuating a pedal force transmitting element on which an actuating force (pedal force) is exerted when the brake system is actuated by the vehicle driver, which pedal force transmitting element is restored to a starting position by a return spring when the pedal is not actuated and which is guided displaceably along an actuation axis in a hydraulic retaining piston which delimits a hydraulic retaining chamber in a housing,
b) a travel detecting device which detects the actuation travel of the pedal force transmitting element,
c) a travel simulator which, in the brake-by-wire operating mode, communicates the usual brake pedal feel to the vehicle driver, which is in force-transmitting communication with the pedal force transmitting element and the effect of which can be switched off in the fall-back operating mode,
d) an electrohydraulic pressure generating device which delivers a brake system pressure,
e) electrically controllable pressure modulation valves for setting wheel-individual brake pressures which are derived from the brake system pressure, the pressure modulation valves delivering or transmitting the brake system pressure in the unactivated state,
f) dividing piston devices which on a first dividing piston surface are subjected to the pressure set or transmitted by the pressure modulation valves, and on a second dividing piston surface build up a pressure which is transmitted via hydraulic connections to the wheel brakes,
g) activating elements for mechanically activating the dividing piston devices, and
h) an electronic control and regulation unit.
A prior art brake system of the general type as described above is known, for example, from the international patent application WO 01/72567 A1. The relatively complicated and costly configuration of the electrohydraulic means for setting the pressures impinging on the dividing pistons, in which a pair of pressure modulation valves is allocated to each dividing piston, is regarded as disadvantageous in the known brake system.
It is therefore the object of the present invention to achieve a simplification of the structure of the brake system of the type mentioned in the introduction, and to propose a brake system in which, especially in the area of the electrohydraulic means for setting the pressures impinging on the dividing pistons, a substantial constructional simplification and a reduction of manufacturing costs are achieved.
This object is achieved according to the invention in that the first dividing piston surface and the second dividing piston surface are formed on a first dividing piston portion, and the first dividing piston surface delimits with a third dividing piston surface formed on a second dividing piston portion an intermediate chamber which is connected to the electrohydraulic pressure generating device via one pressure modulation valve in each case, by means of which pressure modulation valve both a pressure build-up and a pressure reduction are effected in the intermediate chamber. Advantageous developments of the subject matter of the invention are described herein.